Report error codes are used to record errors on the final report, and are generally just expanded versions of the parent error code for communicating the error information in a form more suitable for the printed report.
To use an error code it must first have been registered in the Error Codes section. New error codes can be entered using the 'new' link in the 'Add new entry' section, or via the 'Error codes' link in the Quick links, and can then be configured using the 'add' link under the 'On report' column.